[plt-scheme] function `eval-compile-time-part-of-top-level'

Hello everybody, 

I am trying to build an error checker in the style of the DrScheme
Check Syntax tool.

Inspiring myself from syncheck.ss, I was able to add my own button to
the button bar. I am now trying to understand the 100 lines or so, in
the body in the `button-callback' function, that sets up the code-text
expansion.

In there, there is a call to `eval-compile-time-part-of-top-level'
whose purpose eludes me. What does it do? What is it for? 

The documentation says :

"
  (eval-compile-time-part-of-top-level syntax) : evaluates 
  expansion-time code in the fully expanded top-level expression
  represented by `syntax' (or a part of it, in the case of `begin'
  expressions). The expansion-time side might affect the compilation
  of later top-level expressions. For examples, if `syntax' is a
  `require' expression, then `namespace-require/expansion-time' is used
  on each require specificcation in the form. Normally, this function
  is used only by `expand-top-level-with-compile-time-evals'
"

I am not sure I understand the issue being discussed here. Plus, the
last sentence more or less says this function should not be
used.

Can somebody shine light?

-- 
  "In Google non est, ergo non est." 

- Guillaume